Feat[BMQ]: Add authentication on SDK

[emelialei88]

Summary

This PR introduces optional client authentication (and scheduled re‑authentication) into the BlazingMQ SDK by inserting an AuthenticatedChannelFactory layer between the existing stat and negotiated channel factories. When a TCP channel reaches e_CHANNEL_UP, the factory performs an authentication exchange before exposing the channel to higher layers. If the broker’s response provides a lifetime, a re‑authentication timer is scheduled; it is cancelled automatically on channel loss and re-established after reconnect.

Key Points

• Added AuthenticatedChannelFactory to run an auth handshake transparently after connection.
• Introduced support for a user-supplied credential callback SessionOptions::setAuthnCredentialCb.
  • If not provided, behavior is unchanged (fully backward compatible).
• Authentication requests are treated as non-buffered (never replayed across disconnects).
• Re-authentication is scheduled based on the lifetime returned in the broker's response and safely cancelled on channel down.

Example

auto authnFunc = [](bsl::ostream&) -> bsl::optional<bmqt::AuthnCredential> {
    bsl::string data = "user1:password1";
    bsl::string mechanism = "Basic";
    bmqt::AuthnCredential cred(mechanism, bsl::vector<char>(data.begin(), data.end()));
    return cred;
};
sessionOptions.setAuthnCredentialCb(authnFunc);